1. Field of the Invention
The present invention relates to an electronic paper display device, a manufacturing method and a driving method thereof.
2. Discussion of the Related Art
An electronic paper display device is a core device to realize a flexible display. The electronic paper display device is based on electrophoresis in which an electromagnetic field is applied to a conductive material such that the conductive material has mobility. Micro particles having conductivity are distributed between thin-type flexible substrates, and positions of the micro particles (or toner particles) are changed due to the change of the polarities of an electromagnetic field, whereby data is displayed.
The technical approach to realize the electronic paper may be accomplished using liquid crystals, organic electro luminescence (EL), reflective film reflection-type display, electrophoresis, twist balls, or mechanical reflection-type display. Among them, an electronic paper display device using electrophoresis is the most notable technology at the present time. The electrophoresis is a phenomenon in which, when particles are suspended in a medium (a dispersion medium), the particles are electrically charged, and, when an electric field is applied to the charged particles, the particles move to an electrode having opposite charge through the dispersion medium.
FIG. 1 is a sectional view illustrating an electronic paper display device using micro capsules manufactured by E-Ink Corporation. As shown in FIG. 1, transparent micro capsules 100 having a diameter of 200 to 300 μm, each of which contains specific-color ink particles 103a having a specific electric charge, different-color ink particles (or colored rheological material) 103b having an electric charge opposite to that of the ink particles 103a, and a transparent rheological material 104, are manufactured. The manufactured micro capsules 100 are disposed between upper and lower transparent electrodes 105 and 106 while the micro capsules 100 are mixed with a binder 107, and then voltage is applied to the micro capsules to display characters or images.
However, this structure is a wet-type structure in which the response speed is decreased to approximately 100 ms due to the viscous resistance of the liquid, and therefore, it is difficult to display moving pictures. Furthermore, it is necessary to equally maintain specific gravity between the electrified two-color particles and the rheological material, to prevent cohesion between the electrified two particles, and to carry out additional physical and chemical processes for electric charge attachment, which is required to accomplish electrophoretic mobility. Specifically, it is necessary to additionally carry out a step of introducing a functional group to facilitate the introduction of white color and attachment of an electric charge controlling agent after chemical and physical polymer coating is performed or polymer balls are created. As a result, the process is complicated.
FIG. 2 is a sectional view illustrating a dry-type electronic paper display device. As shown in FIG. 2, the dry-type electronic paper display device includes one or more pixels isolated from each other by barrier ribs 113. Two kinds of electrophoretic particles 116 having different colors and electrification characteristics are encapsulated between transparent substrates 111 and 112 having electrodes 114 and 115 formed at the inner surfaces thereof. Voltage is applied to the upper and lower electrodes 114 and 115 such that the electrophoretic particles collide with each other, and therefore, the particles are charged due to the collision, thereby forming electrophoretic particles. After that, an electric field is applied to the electrified electrophoretic particle groups such that the electrified electrophoretic particle groups can move from the upper and lower electrodes 114 and 115 having different electric potential, whereby pictures are displayed. The dry-type electronic paper display device may further include insulating layers 117 to effectively prevent the electrified electrophoretic particles from being discharged.
FIG. 3 is a graph illustrating the change of reflection rate based on driving voltage in an electronic paper display device. Specifically, FIG. 3 illustrates the change of light reflection rate at the respective cells of the above-described dry-type electronic paper display device as voltage is applied to the first and second electrodes 114 and 115 of the electronic paper display device.
Black and white dry-type particle groups having different electrification characteristics exist in each cell of the dry-type electronic paper display device. When voltage is applied to the first and second electrodes 114 and 115, the respective particles collide with each other with the result that the black particle group is charged with positive charges, whereas the white particle group is charged with negative charges, which will be described below in more detail.
Referring to the drawings, as the magnitude of voltage applied to the first and second electrodes 114 and 115 is increased from V1 to V2, the white particle group charged with the negative charges gradually moves to the upper electrode 114 having the positive potential. As a result, the light reflection rate of the cell is increased.
When voltage of more than V2 is applied to the first and second electrodes 114 and 115, the white particle group existing in the cell moves to the upper electrode 114. As a result, the light reflection rate is maximized.
When voltage of less than V1 is applied to the first and second electrodes 114 and 115, on the other hand, the black particle group remains at the upper electrode 114, and the white particle group cannot move to the upper electrode 114. As a result, the light reflection rate is minimized. In other words, the cell displays black.
The V1 voltage means a threshold voltage at which the light reflection rate of the cell begins to be changed, i.e., at which the white particle group located at the lower electrode 115 begins to move to the upper electrode 114. The V2 voltage means a voltage at which the white particle group existing in the cell can move to the upper electrode 114 while the black particle group can move to the lower electrode 115.
Unlike the wet-type electronic paper display device, the dry-type electronic paper display device has a threshold voltage of a predetermined voltage level necessary to move the black and white particle groups in the cell.
For this reason, only when a pulse having a driving voltage of V2, which is greater than the threshold voltage, is selectively applied to the upper electrode (data electrode) 114 and the lower electrode (scan electrode) 115, desired data can be displayed.
Consequently, a driving voltage pulse having a large voltage level corresponding to V2 must be applied in the electronic paper display device, and therefore, the internal voltage of driving devices must be large. Furthermore, time necessary to generate the driving voltage pulse having the large voltage level is increased with the result that the response speed is lowered.